The invention relates broadly to the section of a furnace in which a continuous web, such as a strip of metal, is cooled and, in particular, to the gas jet cooling section of an annealing furnace that is used in the production of high strength steels.
In such annealing furnaces, a continuous strip of metal travels successively through separate heating and soaking sections before it enters the gas jet cooling section, so-called because the hot metal strip is cooled from a temperature of, for example, 1400.degree. F. to 1000.degree. F. by jets or streams of a special protective cooling gas which are impinged against the strip of metal as it moves in one or more directions through the gas jet cooling section. The cooling of the strip is relative in that the strip is at an extremely high temperature of 1000.degree. F. as it exits the gas jet cooling section for subsequent quenching and reheating. The temperature of the cooling gas is an important factor and is dependent on, for example, the strip cooling required, the rate of strip production desired, and the volume of the cooling gas used.
Better, more uniform cooling is achieved by contacting the trip of metal with a large mass flow of gas at a temperature which approaches or more nearly equals the temperature to which the strip is desired to be cooled, rather than contacting the strip with a small mass flow of gas at a substantially lower temperature. Translated to the example indicated above, it is advantageous to cool the strip to 1000.degree. F. by contacting the strip with a sufficiently large mass of cooling gas at a temperature of, for example, 900.degree. F., rather than contacting the strip with a much smaller mass flow of cooling gas at a much lower temperature of, for example, 300.degree. F. It can be appreciated from the above, that the cooling gas referred to in this application may be at temperatures which would be considered extremely high in other processes.
The invention is specifically designed to maintain more uniform temperatures within the gas jet cooling section of an annealing furnace by the elimination or substantial reduction of cold spots which occur in such sections and adversely affect the uniformity of the temperature conditioning of the strip of metal as it passes through this section of the furnace.
Briefly stated, the invention is in the cooling section of an annealing furnace, which section includes a vertically elongated chamber which is sealed from the ambient atmosphere and through which a continuous element, such as a strip or sheet of metal, is passed in one or more directions. Means are provided for impinging confronting streams of cooling gas against opposite sides of the element as it passes vertically through the chamber. Means disposed alongside the chamber in communicating relation with the chamber, are supplied for cooling gas removed from the chamber, prior to the reuse of the gas for impingement against the traveling element. Means are provided for eliminating the backflow of gas, cooled by the gas cooling means, into the chamber to create within the chamber, cold spots which affect the uniform treatment of the element, since the circulation of gas used to cool the element is what might be called, a continuous closed loop system, i.e. the gas impinged against the traveling element in the chamber is initially removed from the chamber, cooled, and then recirculated to the chamber for impingement against the element.